Are there any precautions a carrier of hemophilia should take if she becomes pregnant?

Depends. Some women who are carriers for hemophilia a can actually have low factor viii levels, enough that they could have symptoms. Because it is an easy test, i would actually check a factor viii level, especially if a person has never been "hemodynamically challenged" before, in other words had surgery that might have uncovered a low factor viii level.
Yes. Carriers of hemophilia should have their future partner also tested for the illness. If both parents carry the disease; their children will be more likely to also have the disease.